This invention relates to an information reproducing device for reproducing data information contained in audio band signals of a video disk, and more pareticularly to an information reproducing device for reproducing a modulated video band signal and a modulated audio band signal recorded on a video disk, said modulated audio band signal containing digital information including a computer program.
A video disk has recorded thereon FM moduldated video signals and one or more FM modulated audio band signals as well as data information.
A conventional video disk reproducing device is illustrated in FIG. 1. Video signals and audio band signals recorded on a video disk 1 are converted into electric signals after being picked up by means of pickup 2 and then amplified by preamplifier 3. The video signals are then supplied to and demodulated by video demodulator 4, thus forming a video signal reproducing circuit. Meanwhile, the two audio band signals amplified and FM modulated by preamplifier 3 are supplied to and demodulated by an audio first channel demodulator 7 and an audio second channel demodulator 10, thus forming audio signal reproducing circuits. Drop-outs are detected at drop-out detecting circuits 8 and 11 respectively connected to said demodulators 7 and 10 and are compensated for by preholding or the like at drop-out compensating circuits 9 and 12 respectively connected to said demodualtors 7 and 10 and said drop-out detecting circuits 8 ad 11. The first and second channel audio band signals for which drop-outs have been compensated are then outputted from switch 13 which switched among a stereo mode, a first channel monaural mode, a second channel monaural mode, and so on. The second channel signals are supplied to microprocessor 6 of a reproducing system.
Meanwhile, data included in the video signals modulated by the video demodulator 4 are read by a data reader 5 and fed to the microprocessor 6. The audio band signals may sometimes contain, in addition to voices, digital data information such as a production program for a reproducing system indicated by binary high and low signals, a program for activating any other device such as, for example, a personal computer 14, and so on.
Generally, the FSK modulating system wherein data are transmitted by phase information of rectangular waves having high and low levels is employed for such digital data information. After such data are inputted to and stored in the microprocessor 6 of the reproducer, the reproducing system operates in accordance with a program of the digital data information.
On the other hand, where the output is supplied to the personal computer 14, the digital data information recorded on the video disk are fed to the personal computer 14 as described hereinabove. For example, a program of a game program or the like can be transmitted by such digital data information.
In the information reproducing device which reproduces a video disk which has such digital data information additionally recorded thereon as described above, the drop-out detection sensitivity is very high since it is adjusted for average audio signals, and hence drop-out compensation is performed even when there is a low level of drop-outs in comparison with the digital data information of a high level while a difference between high and low levels is constant. As a result, the traditional information reproducing device has a drawback that the phase of the digital data information is disturbed by such drop-out compensation, resulting in deterioration of a data reading faculty of a microprocessor 6.
FIGS. 2A, 2B and 2C illustrate examples of outputs from audio second channel demodulator 10, the drop-out detecting circuit 11 and the drop-out compensating circuit 12 of FIG. 1, respectively.